1. Field of the Invention
The present invention relates to a system for in-situ remediation of contaminated groundwater and soil. In particular the present invention relates to stabilizing toxic metals in groundwater and soil.
2. Discussion of the Background
Contaminated groundwater and soil pose serious health problems if local groundwater is used as a source of drinking water or the soil is used for growing crops and vegetation. Preventing contamination in the groundwater and soil from contaminating the drinking water and crops can be high.
Contaminated soil is usually removed by excavation; contaminated groundwater may be removed at times along with excavated soil and sometimes by pumping groundwater to the surface of the earth for treatment. Both excavating and pumping, although direct methods of dealing with the contamination, are expensive.
Recently, methods for drilling horizontal wells have been developed. In "Radial Wells and Hazardous Waste Sites," Wade Dickinson, R. Wayne Dickinson and Peter A. Mote, described a method for drilling horizontal wells for remediation of contaminated groundwater. "Horizontal" drilling is directional drilling that deviates significantly from the vertical. Wells placed into the contaminated area may be used for extraction of contaminated groundwater or to inject various treatment substances.
In U.S. Pat. No. 4,832,122. Corey, et al. describe a method and system for removing volatile contaminants from a subsurface plume of contamination. This system comprises two sets of wells, a well for injecting a fluid into a saturated zone on one side of or within the plume and an extracting well for collecting the fluid together with volatilized contaminants from the plume on the other side of, above or within the plume. The fluid enables the volatile contaminants to be volatilized and carried therewith through the ground to the extracting well. A system in accordance with that described in U.S. Pat. No. 4,832,122 was put to use on an area of contaminated groundwater beneath the location of an abandoned process sewer line that was known to have leaked chlorinated solvents. The site was carefully characterized and monitored using surface and borehole geophysics, cross hole geophysical tomography, chemical analysis of soil, soil gas and groundwater, microbial characterization of soil and water, and pressure monitoring in all affected areas. The total concentration of chlorinated solvents decreased rapidly during the first two days of operation and stabilized after approximately three days. Initial concentrations were as high as 5000 ppm in the gas and the total concentration stabilized at approximately 300 rpm. This concentration represents an extraction rate of approximately 100 to 140 pounds of solvent per day. The vacuum extraction process removed contaminants at a rate of 109 pounds per day; injection of air at the medium and high injection rates appears to result in the stripping/removal of an additional twenty pounds of solvents per day from the groundwater and the vadose zone below the extraction well. Almost 16,000 pounds of contaminant were removed from the vadose zone and groundwater at the site during the testing period. The system described by Corey, et al. is apparently effective for removing volatilizable contaminants in subsurface plumes but would not be effective for remediating nonvolatile contaminants such as metals.
There is a need for methods to remediate other contaminants in groundwater and soil.